The present invention relates generally to the field of electronic data storage and retrieval, and more particularly to a perpendicular magnetic writer having a return pole that is laminated to suppress side track erasure.
In an electronic data storage and retrieval system, a transducing head typically includes a writer for storing magnetically-encoded information on a magnetic medium and a reader for retrieving that magnetically-encoded information from the magnetic medium. The reader typically includes two shields and a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the magnetic medium causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
For a perpendicular recording head, the writer typically includes a main pole and a return pole which are connected to each other at a back end by a back yoke (or back via), and which are separated from each other at a surface of the writer opposite the back end by a gap layer. One or more layers of conductive coils are positioned between the main and return poles and are encapsulated by insulating layers. Often, the writer and the reader are arranged in a merged configuration in which a shared pole serves as both the top shield of the reader and the return pole of the writer. Alternately, the writer and reader may be arranged in a piggy back configuration in which top shield of the reader and the return pole of the writer are separated by a layer of a nonmagnetic material.
A perpendicular recording medium for use with a perpendicular recording head includes a storage layer and soft underlayer. The storage layer of the medium preferably has a high coercivity and perpendicular anisotropy; that is, its magnetization is preferably held in a direction substantially normal to a surface of the medium. The soft magnetic underlayer of the medium preferably has a high permeability and a substantially in-plane orientation of the easy axis.
To write data to the perpendicular magnetic medium, an electric current is caused to flow through the conductive coils to induce a magnetic field across the write gap between the main and return poles. In operation, the underlayer of the magnetic medium acts as a third pole of the writer such that the magnetic field bridges two gaps—the gap between the main pole and the underlayer and the gap between the underlayer and the return pole—with the magnetic field passing twice through the storage layer of the magnetic media. As connoted by their names, the main pole is used to physically write data to the magnetic medium, while the return pole provides only a return path for the magnetic field generated by the main pole. Thus, the magnetic field traversing the gap between the main pole and the underlayer is preferably strong enough to cause a bit to be recorded to the media while the magnetic field traversing the gap between the underlayer and the return pole is not.
To ensure that the magnetic field traversing the gap between the underlayer of the medium and the return pole does not contribute to the data written to the magnetic medium, the return pole conventionally has been formed of a lower magnetic moment material than the main pole and has been configured with a larger area at the media facing surface than the main pole.
Despite this larger surface area, the strength of the magnetic field affecting the magnetic medium under the return pole is nonetheless sufficient to overcome a nucleation field of magnetic medium. This results because the magnetic flux throughout the cross-section of the return pole is not uniform, but is instead concentrated along the edges of each element of the writer. This concentration along the edges is caused by various factors, including surface anisotropy, an edge pinning effect, and a skin effect. Further, this concentration of magnetic flux at the edges of the return pole may result in a sizable magnetic field being produced at the edges of the return pole when the write current is on. In fact, the magnetic field may be as great as 10-80% of the saturation magnetic flux density (Bs) of the return pole's soft materials. Further, this magnetic field may be large enough to cause undesired side track erasure on the magnetic medium. To the extent that the field is not strong enough to actually erase the magnetic medium below the return pole, the side-writing may be significant enough to accelerate the magnetization decay process, leading to a non-negligible threat to the long term data retention of the magnetic medium